Continuous chilling process for dewaxing



May 28, 1940. v. vooRHEEs l CONTINUOUS CHILLING PRocEvss vFOR nEwAxING Filed March 18, 1938 INVENTOR veer Voor' ATTORNEY j lPQhIII .NIN

Patented May 28, 1940 UNITED STATES v CONTINUOUS CHILLING PROCESS FOR DEWAXIN Vanderveer Voorhees,v1lammond, Ind., assignor tov .Standard Oil Company, Chicago, lll., a corporation of Indiana Application March 18, 1938, Serial No. 196,608 y 1o claims. (ci. 19e-1s) 6 It is extremely important in dewaxing processes that the wax be crystallized from the oil in readily separable form so that when the chilled wax slurry is filtered, settledor centrifuged a substantially oil-free wax and a large yieldof de- 10 waxed (low pour point) oil will be obtained. It

has been found that propane is an excellent diluent for accomplishing these results, but in all propane dewaxing plants that have been constructed, it has been necessary to employ batch chilling in order to prevent the flashing of propane at a point of pressure release with consequent yshock chilling. An object of my invention is to provide a continuous method of chilling a wax mixture' which will avoidshock chllingand which will produce readily separable wax crystals and thereby lead to the production of large oil yields and oil-free waxes.

A further object of the invention is to provide a simple and efficient dewaxing system which will involve lower capital expenditures and lower operating costs than dewaxing systems heretofore known. A further object is to increase the uniformity of operation of a dewaxing system and the uniformity of products produced by said system.

A further object is vtoprovide means for accurately controlling the temperature gradient in continuation-in-part of my prior application Serial No. 733,271, filed June 30, 1934, and issuedA as Patent No. 2,127,708 on August 23, 1938, in 45 which I describe the vaporization of propane from an oil-propane solution at substantially constant pressure, the vaporization being effected by the circulation of a current of inert gas. I have found that carbon dioxide is an ex- 60 cellent inert gas for use in this system, and that the carbon dioxide may be liquefied and then vaporized in the chilling tower to increase the efficiency and effectiveness of the chilling operation. An important feature of my invention is I6 the accurate control of the temperature gradient throughout the chilling tower by the introduction of liquid carbon dioxide in regulated amounts at a plurality of spaced ypoints along the length of the tower, the carbon dioxide being introduced out of contact with the liquid oil-wax mixture. B The carbon dioxide which is thus introduced not only effects chilling by its own vaporization, but

it brings about further vaporization of the propane from the diluted oil-wax mixture at the point of introduction. The carbon Ydioxide and 10 propane vapors leave the top of the towerat about 150 to 200 pounds pressure so that with slight additional compression a substantial part of the propane may be liqueed with ordinary condenser water and the carbon dioxide may be 15 liquefied by contact with the cold 'illtrate The liquei'led carbon dioxide may then be reintroduced at the spaced points along the chilling tower.

'I'he invention will be more clearly understood from the accompanying drawing which forms a 20 part of this speciilcation and which diagrammatically illustrates my improved chilling and dewaxing system. l

The invention will be described in connection with the dewaxing of a deasphalted Mid-Conti- 25 nent residual lubricating oil stock, but it should be understood that the invention is equally applicable to distillate stocks and to crudes vfrom any and all sources. In my preferred embodiment I use propane as a diluent, but it should be under- 30 stood that other normally gaseous hydrocarbons, such as ethane, iso-butane, normal butane, ethylene, propylene, the butylenes and mixtures of any two or more of these hydrocarbons with each other or with other diluents. The invention is also applicable to the use of non-hydrocarbon diluents, particularly wax anti-solventsl such y as dimethyl ether, sulfur dioxide, etc. Certain aspects of the invention may be employed-with less volatile diluents such as naphthas, acetone, 40 methyl ethyl ketone, benzol acetone mixtures, methyl ethyl ketone benzol mixtures and other known dewaxing diluents.

vThe deasphalted residual lubricating oil stock is charged to the system through line l0 and 4 5 mixed with about 2 to 4 volumes of propane withdrawn from storage tank ll through line l2. Suitable pumps in lines lIll and I2 proportion the mixture of -oil and propane and eiect the -introduction of this mixture through line I3 into cooling tower I4 which is maintained at a pressure of about 150 to 200 pounds per square inch. It should be understood, however, that the pressure in this tower will vary with different diluents and different chilling temperatures and may r range from about 50 to 250 pounds per square inch. With the above-described propane mixture introduced at a temperature'ol` about 100 F. and Withdrawnfrom the base of the tower at a temperature of about 40 F., I prefer to operate the tower at a pressui'e of about 150 pounds per square inch. It should be understood that the oil-propane mixture may be heated to temperatures of to 190 F. and subsequently cooled to about 80 to 100 F. in cooling water ex changers before being introduced into the top of the chilling tower.

Chilling tower I4 is preferably provided with a series of alternating baille plates I6,'which are so arranged that the liquids will cascade from plate to plate in the course of their now from the top to the bottom of the tower. Along the length of the tower I provide a carbon dioxide header I6 and from this header a plurality of valved carbon dioxide injectors I1 lead to spaced points in the tower underneath said spaced baille plates I5. 'Ihe liquefied gas is introduced out of direct contact with liquids in the tower, so that shock chilling is avoided.

As the propane-oil solution enters the tower through line I3 there will be no appreciable flashing of propane because 'of the high pressure which is maintained within the tower. Propane will evaporate, however, from this mixture into the upwardly-flowing stream of carbon dioxide, and this gradual and uniform vaporization of propane will effect the desired continuous refrigeration. To assure the uniformity of cooling throughout the length of the tower I introduce the carbon dioxide in regulated amounts at spaced points along the entire length of the tower. The carbon dioxide thus introduced through injectors I'I effects a certain amount of cooling due to the absorbed heat of vaporization when the liquid carbon dioxide is vaporized. Furthermore, at each point of introduction there will be provided a carbon dioxide atmosphere into which propane may vaporlze, so that the vaporization of propane is augmented by its partial pressure. 'Ihe amount of cooling at any particular portion of the tower can be determined by the amount of liquid carbon dioxide which is introduced at that point, and by proper regulation of valves in injectors I'I, for instance by thermostatic controls Ila, a uniform temperature gradient can be maintained throughout the length of the tower. The valves in injectors I1 are preferably thermostatically controlled in accordance with tower temperature so that regulation is continuous and automatic.

For a tower pressure of about pounds the slurry withdrawn from the base of the tower will be at a temperature of about 40 F., and it may be introduced directly through line I8 to the bowl of continuous filter I 9, although any conventional separating means may be used. The filter is preferably of the type described in U. S. Patent 2,050,007. A feature of my invention is the use of the tower pressure for operating the lter so that no mechanical pumps of any kind are required. This is important because mechanical vpumps tend to macerate and destroy the wax crystals, and to make ltration more difficult.

Fltrate is withdrawn through line 2D, heat exchanger 2| and line 22 to high pressure oil still 23 which may be operated at a pressure of about 200 pounds per square inch, and which is provided with a suitable heater such as steam coll 24. Most of the propane and dissolved carbon dioxide is withdrawn through line 25, cooled by condenser water in exchanger 26 and introduced through line 2l into propane separator 28. Liquid pi'opane is returned through line 29 to propane storage tank II and the carbon dioxide, together with some vaporized propane is withdrawn through line 30 and introduced, with the carbon dioxide .and propane' leaving tower I4 through line 3I into the suction side of compressor 32. It should be noted that the pressure of the carbon dioxide and propane in line 3| is substantially the same as'that in line 30. although it may be necessary to employ a pressure ieduction valve in the latter line.

Compressor 32 raises the pressure of the carbon dioxide and propane to about 300 to 750 pounds per square inch, depending somewhat upon the temperature to which the compressed gases are cooled for liquefaction. The compressed gases are first cooled by condensing water in cooler 33 and any propane which is liquefied may be separated from uncondensed carbon dioxide by closing valve 34 and by-passing the mixture through line 35 to propane trap 36, the separated propane being introduced through line 3l and pressure-reducing valve 38 back into the top of the tower, and the carbon dioxide be ing withdrawn from the top of trap 36 through line 39 to line 40. Alternatively, valve 34 may be left open and the valves in lines 35 and 39 may be closed, so that both propane and carbon dioxide are passed through heat exchanger 2l. In this heat exchanger the carbon dioxide is brought into counter-current thermal contact with cold filtrate soV that the filtrate is appreciably warmed and the carbon dioxide is cooled and liquefied. The liquid carbon dioxide which may be at a temperature of about +30 F. to 30" F. is introduced through line 4I to trap 42, and the liquid carbon dioxide from the base of this trap supplies header I6 which has been hereinabove described. Any uncondensed gases which collect in the upper part of this trap may be vented through release valve 43 and line 44.

In my cooling and dewaxing system there is no necessity for obtaining a sharp separation of propane from carbon dioxide. The propane which is carried with the carbon dioxide thru line 40 (i. e. is not separated in trap 36) is miscible with the liquid carbon dioxide and this liquefied gas mixture is referred to as carbon dioxide even tho it may contain large amounts of propane. The propane itself serves a useful function when vaporized from injectors I'I. To obtain the maximum benefits from my system, however, a large proportion, at least, of the liquefied gas should be characterized by a vapor pressure which is substantially higher than that of the diluent employed.

Returning now to the propane recovery system, the depropanized oil from highv pressure still 23 is withdrawn through line 45 and pressure-reducing valve 4B to low pressure oil still 4l which is provided with a suitable heater such as steam coil 48. Vapors from the top of still 4l are withdrawn through line 49, compressed by compressor 50 and introduced into line 25, cooler 26 and propane separator 28, as hereinabove described. Dewaxed oil is withdrawn from the base of low pressure still 4'I through line 5I to storage or to any suitable finishing processes. It should be understood, of course, that this oil may be stripped with steam and blown bright with air or` inert gas prior to its removal from the system, and that the vapors removed by the stripping operations may be recovered and returned to the system.

Ther wax slurry which is removed from the filter through line 52 is introduced into high pressure wax still 53 which is provided with a suitable heater such as steam coill 54, andwhich is preferably operated at a'pressure ofabout 200 pounds per square inch. Propane and dissolved carbon dioxide from the top of `this tower may 'be withdrawn through line 55 to line 25. De-

steam coil 59. Propane from the low pressure still is Withdrawn through line 60 to line 49 and the finally depropanized wax is withdrawn to storage orv to sweating or finishing systems through line 6I. v

It should be particularly noted that the carbon dioxide and propane vapors which are removed from the top of tower I4 and which are returned through line 30 to line 3| are at a pressure of about to 200 pounds per square inch. This means that compressor 32 will have relatively light duty since it is only'necessary to raise the pressure of these gases to about 300 to '750 pounds, preferably about 500 pounds.

A small amount of the carbon dioxide will inevitably be carried with the propane into storage tank II, and a small amount of the propane will inevitably be carried with the liquid carbon dioxide through trap 42 and header I6. The amount of gases or vapors thus dissolved do not deleteriously effect the system and as herelnabove pointed out no sharp fractionation is necessary. between the carbon dioxide and proane.

p It should be understood that While I have described carbon dioxide as a preferred example of my auxiliary refrigerant, the invention may also be practiced with other inert gases. It is important, however, that the gas have a sufficiently high vapor pressure under the desired chilling conditions to effect refrigeration under the pressure maintained in tower I4, and when propane or other normally gaseous diluent is employed it is important that the vapor pressure practice additional desired heat exchangers, au-

tomatic controls and engineering expedients which are well-known to those skilled in the art will be employed in accordance with practice well-known to those skilled in the art. I do not limit myself to the preferredembodiment orto the details hereinabove set forth except as defined by the following claims which should be construed as broadly as the prior art will permit.

I claim:

1. The method of dewaxing petroleum oil which comprises dissolving a wax-bearing petroleum oil in a diluent, introducing said diluentoil solution at the top of a chilling zone and cascading the solution from the top to the bottom of said zone, injecting a liquefied gas into said zone at spaced points along the length thereof to effect chilling and the liberation of gasesand vapors, said gas having a vapor pressure substantially higher than the vapor pressure of the diluent, regulating the amounts of injected liquefied gas introduced at each point to maintain a substantially uniform temperature gradient throughout the zone, withdrawing chilled slurry from the base of said zone, mechanically separating Wax-from said slurry and removing both gas and diluent from the separated Wax and oil respectively. I

2. The method of claim l wherein the liquefied gas is introduced into the chilling zonev out of direct contact with 'liquids in said zone.

3. The method of claim 1 which includes the steps of withdrawing gases and vapors from ythe top of said chilling zone, compressing said vapors, liquefying the compressed gasesfand vapors, separating liquid diluent l"from liquefied gases, re-

`turning liquefied diluent tothe top of said chilling zone, and returning said liquefied gases at spaced points along said chilling zone.

4. The method of claim 1 wherein the diluent is propane and the liquefied gas is carbon dioxide.

5. The method of continuously chilling a di` luted wax-oil to eiect the solidification of wax in separable form which comprises introducing said diluted waxy oil at the top of a chilling zone, cascading said diluted oil from the top to the bottom of said chilling zone, introducing at spaced points along said chilling zone a liquefied gas of substantially higher vapor pressure than the vapor pressure of the diluent, whereby the liquefied gas is vaporized throughout the length of the chilling zone, and whereby the vaporized liquefied gas promotesA partial vaporization of diluent throughout the chilling zone, withdrawing chilled slurry from the base of said chilling zone, separating wax from diluted oil, removing and compressing gases and vapors from the top of said chilling zone, cooling said compressed gases and vapors to obtain liquefaction thereof, and returning the liquefied gases at spaced points along said cooling zone.

6. The method of claim 5 which includes the further step of 'separating liquefied diluent from theliquef'ied -gas and returning the liquefied diluent at the upper part of said chilling zone.

7. The method of claim 5 which includes the further steps of distilling diluent and gas from wax and wax-free diluted oil, respectively, separating diluent containing dissolved gas from uncondensed gas and diluent vapors, diluting further quantities of oil with said diluent, and combining said uncondensed gas and diluent vapors with the gas and diluent vapors leaving the top of the chilling zone, and entering the compression step. y

8. A continuous propane dewaxing process which comprises diluting a waxy oil withl propane to form a waxy oil solution, introducing said solution at the top of a chilling zone, cascading said solution from the top of said chilling zone to the bottom thereof, introducing liquefied carbon dioxide at spaced points along said chilling zone, whereby the solution is chilled by vaporization of the carbon dioxide and by vaporization of propane into carbon dioxide gas throughout the length of the chilling zone, withdrawing a wax slurry from the 'base of the chilling zone,

mechanically separatingwax from the diluted oil,

faction of the carbonl dioxide, and returning the 75 liquefied carbon dioxide at said spaced points along said chilling zone.

9. The method of claim 8 which includes the further steps of distilling propane and .carbon dioxide from said wax and diluted oil respectively, cooling said distilled carbon dioxide and propane to eiect the liquefaction of most of the propane, returning the liqueed propane to the original waxy oil solution step and compressing said gaseous carbon dioxide and propane along with the carbon dioxide and propane from the top of the chilling zone.

10. The method of operating a propane-carbon dioxide dewaxing system which comprises diluting a waxy oil with propane, continuously chilling said propane-waxy oil mixture in a chilling zone maintained at a pressure of about 100 to 200 pounds per square inch by introducing liqueed zon separating said slurry into wax and diluted oil, ecovering propane and carbon dioxide from said wax and diluted oil respectively at a pressure of about 100 to 200 pounds per square inch,

compressing said recovered carbon dioxide and 10 propane together with the carbon dioxide and propane from the chilling zone, cooling the compressed carbon dioxide and propane to eiect liquefaction thereof, and returning said liquefied carbon dioxide and said propane to said chilling 15 Zone.

VANDERVEER VOORHEES. 

